1. Field of the Invention
The present invention relates to a fuel cell comprising fuel cell units each of which is interposed by separators.
2. Description of the Related Art
A solid polymer fuel cell is known, which is designed, for example, as a fuel cell stack comprising fuel cell units each of which includes an electrolyte composed of a polymer ion exchange membrane (cation exchange membrane), an anode electrode, and a cathode electrode, the electrodes being arranged on both sides of the electrolyte respectively, and the fuel cell units being interposed by separators.
Such a fuel cell is operated as follows. That is, the fuel gas, for example, hydrogen-containing gas, which is supplied to the anode electrode, is converted into hydrogen ion on the catalyst electrode, and it is migrated toward the cathode electrode via the electrolyte which is appropriately humidified. Electrons are generated during this process, and they are extracted by an external circuit to be utilized as DC electric energy. The oxygen-containing gas, for example, oxygen gas or air is supplied to the cathode electrode. Therefore, the hydrogen ion, the electron, and the oxygen react on the cathode electrode to produce water.
The fuel cell as described above adopts a technique as disclosed, for example, in Japanese Laid-Open Patent Publication No. 8-203546, in order that the fuel gas is supplied to the anode electrode and the oxygen-containing gas is supplied to the cathode electrode.
That is, as shown in FIG. 7, an anode electrode 4 and a cathode electrode 5, each of which has a catalyst layer 2 and a gas diffusion layer 3, are provided on both sides of an ion exchange membrane 1. Separators 6, 7 are arranged at the outside of the anode electrode 4 and the cathode electrode 5. Flow passage grooves 6a, 7a for supplying the fuel gas and the oxygen-containing gas respectively are formed at flat surface portions of the separators 6, 7 to make contact with the anode electrode 4 and the cathode electrode 5 respectively.
However, the conventional technique described above includes lands 6b, 7b which are provided between the respective flow passage grooves 6a, 7a of the separators 6, 7. The lands 6b, 7b make tight contact with the respective gas diffusion layers 3 of the anode electrode 4 and the cathode electrode 5. Therefore, when the fuel gas and the oxygen-containing gas are supplied to the flow passage grooves 6a, 7a, the diffusion performance is deteriorated at portions of the gas diffusion layers 3 which make contact with the lands 6b, 7b. Portions 2a of the catalyst layers 2, which correspond to the lands 6b, 7b, are not utilized for the reaction.
Therefore, a problem is pointed out that the effective reaction area of the catalyst layer 2 is decreased, and the power generation performance is lowered. In view of this fact, an arrangement may be conceived, in which the effective reaction area of the catalyst layer 2 is increased by increasing the thickness of the gas diffusion layer 3. However, such an arrangement causes another problem in that the electric resistance is consequently increased, and the size of the entire fuel cell stack is increased in the stacking direction.
A principal object of the present invention is to provide a fuel cell which is suitable for realization of a miniaturized size, in which the gas diffusion performance is enhanced, and thus the effective reaction area is increased.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.